Bulletin of the Bureau of Standards Volume 6, Nos. 116-142

Bulletin of the Bureau of Standards Volume 6, Nos. 116-142

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1910 edition. Excerpt: ...in emissivity in the deep red, when two lamps are apparently matched in color. As a finale to this discussion of the inapplicability of the color match (or for that matter any other device than a spectroradiometer) for predicting what happens in one part of the spectrum from observed conditions in another region, let us select the Welsbach mantle and also the same material formed into an electrically heated rod. Let us suppose that it is difficult to estimate the efficiency of the mantle; we therefore select the electrically heated rod and determine the watts per candle. Assuming that the emissivityof the oxides is dominated by surface conditions, as in metals (in which the absorption coefficient is extremely large as compared with oxides), we decide from our observations on the electrically heated rod that the same relation of watts per candle must hold in the mantle. We might even conclude that, on account of the cellular structure of the mantle, it is "blacker" than the smooth rod, and hence is less efficient as a source of light. To what absurdities such assumptions can lead will be noticed in Fig. 12, which shows the distribution of energy in the spectrum of the Welsbach mantle, curve b (data from Rubens), and of the same material (99 p. c. thoria 1 p. c. ceria) in the form of a rod heated electrically. In the latter, curve a, Fig. 12, the vertical scale is one-third that of the mantle. It will be observed that the mantle is almost lacking in infra-red radiation. The reason for this is not difficult to find. The oxides are"transparent media," and hence the emissivity is a function of the thickness rather than of the reflecting power (high absorption coefficient), as in metals. The small amount of cerium-oxide, which has a...show more

Product details

  • Paperback | 150 pages
  • 189 x 246 x 8mm | 281g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236494075
  • 9781236494078